Anionic polymerization of olefins is a well-known process and is used in a variety of industries. Solvents and monomers used in the anionic polymerization of ethylenic and vinylic monomers (typically styrenic and dienic monomers) should be thoroughly dried to avoid any deactivation of the propagating active centers before the end of the polymerization reaction. The drying process requires highly efficient agents since the concentration of active species is very low and any residual amount of impurities is sufficient to significantly perturb the polymerization and the control of polymer molar masses and chain functionalization. For example, to achieve the polymerization of polystyrene with an expected and controlled molar mass in the range 10,000 to 100,000 g/mol, and working at monomer concentration of 1 mol/l, the initiator concentration should be in the range 10−2 to 10−3 mol/l. This means that a concentration in impurities less than 10% of the active species concentration should be present to get acceptable results. Efficient drying agents should also be able to remove trace impurities in the solvent and in the monomer. Generally, the drying conditions applied to the solvent and to the monomers must be different to avoid any risk of unwanted polymerization of monomers.
Typical drying agents used for solvents at laboratory scale are butyllithium, polystyryllithium, diphenylhexyllithium, activated sodium or potassium (mirrors or metal wires), and sodium-potassium alloys. Some others, of limited number, can be used both for the solvent and monomer such as dialkylmagnesium, aluminum trialkyls, and calcium hydride (although of limited efficiency). Drying at the industrial scale may also be achieved by passing the solvent and monomer over molecular sieves or over activated alumina.
In most cases the solvents and monomers must be subsequently distilled to remove any traces of drying agent, which may affect the polymerization reaction. After this last operation, the solvents and/or monomers are typically transferred into the polymerization reactor under inert atmosphere and are ready for use. These drying processes are tedious and constitute a strong limitation for the development of anionic polymerization both at laboratory and industrial scales. There is, therefore, a need in the art for effective drying agents and impurity removal for anionic polymerization processes. This invention answers that need.